This invention relates to a method of manufacturing a vacuum-type circuit interrupter and, more particularly, relates to a method of manufacturing the interrupter so as to substantially reduce the number of free particles present within the interrupter during normal operation.
A widely-used type of vacuum interrupter comprises a centrifugally-cast tubular casing of glass and a metal disc cast into the glass and having an exposed portion projecting radially inward of the casing. This interrupter further comprises a tubular metal shield located within the tubular casing in radially-spaced relationship to the casing and mounted on the metal disc.
It has heretofore been recognized that the centrifugal casting operation usually leaves some glass on the disc that should be cleaned off during manufacture in order to avoid its subsequently being chipped off to produce loose particles during operation of the interrupter as a result of mechanical shocks incident to such operation. In U.S. Pat. No. 4,063,991--Farrall et al, assigned to the assignee of the present invention, it is proposed to clean off such residual glass by subjecting the disc first to a grit-blasting action and then to an etching action. This combination of steps does, in fact, significantly reduce the production of loose particles during operation of the interrupter, thereby improving the voltage withstand capabilities of the interrupter. It is advantageous to further improve the voltage withstand capabilities of the interrupter, and this, in fact, is a general object of our invention.